At a previous employer we had a high up executive from Facebook come out to give a presentation.
One of my main take away was that one of FBs big goals was to build a 'knowledge economy'. It struck me as a bit of an odd objective at the time, but I think I am now starting to understand what this means (and it's a little scary).
I am not convinced that parameter type inference is a reason to use flow. I have seen examples where flow fails to report errors because it can't infer the parameter types. I would rather consistency over inference that sometimes works sometimes fails silently.
For example:
function fn(a) {
const {b} = a;
console.log(b.c);
}
fn({});
It is an automated test runner for JS / TS code with a great integration with ides. It has made writing tests and refactoring so much more productive.